Electric valve control circuit



April 1, 1941. J. L. STRATTON 2,237,016

ELECTRIC VALVE CONTROL CIRCUIT I Original Filed June 24, 1939 Inventor":

Jerry L. Str tton, by is Attorney.

Patented Apr. 1, 1941 ELECTRIC VALVE CONTROL CIRCUIT Jerry L. Stratton, Schenectady, General Electric Company,

New York N. Y., assignor to a corporation of Original application June 24, 1939, Serial No.

280,924. Divided and this application August a, 1940, Serial No. 351,976

' s Claima (or 172-239) My invention relates tems and terns for to electric control sysmore particularly to electric valve sys regulating an electrical condition, such as the voltage or current of an associated circuit.

This application is a division of my copending patent application Serial No, 280,924, filed June 24, 1939, entitled Electric control system, and which is assigned to the assignee of this application.

In many industrial applications, it is desired to provide control systems in which an electrical condition, such as the voltage or current of an associated circuit, is maintained constant within a predetermined range of values of a controlling influence so long as the magnitude of the controlling infiuence does not vary beyond a predetermined range, and to establish predetermined maximum and minimum limits the condition if the controlling influence exceeds that range. In accordance with the teachings of my invention described hereinafter, I provide a new and improved electric valve control system which op: crates accurately and positively to effect this type of control.

It is an object of my invention to provide a new and improved electric valve control system,

It is another object or my invention to provide a new and improved electric valve control sys= tern which operates to energize selectively an as sociated control circuit in response to the predominating control voltage produced by the sys item, the control voltages being responsive to dii ferent predetermined controlling influences.

It is a still further object oi my invention to provide a new and improved electric valve for controlling the current transmitted to a control circuit selectively in response to a plurality of relatively variable control potentials which are responsive, respectively, to different prede termined controlling influences.

Briefly stated, in the illustrated embodiment of my invention I provide an electric valve system for controlling selectively the energisation of an associated control circuit in response to a plurality of relatively variable control potentials, each of which varies in response to a different predetermined controlling influence, such as voltage or current of an associated circuit, or in response to the speed or operating condition of an associated dynamo-electric machine.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. The single figure of the drawsystem 'ing, my invention is there represent L ing diagrammatically illustra" oi my invention as applie motor for regulating the spa in Jail controlling or limiting the ma nnurn mum current values transmitted to the am winding thereof.

Referring now to the single figure 0;? the clra I ll i3 to a system for regulating an opera tion, such as the speed, of a machine. The machine to be cc a direct current motor l havi winding 2, a series field winding field winding :3. The shunt field 'wi he energized, if desired, from seoers. of direct current 5. The such as the speed, of the motor I! by suitable translating apparatus a r transmitting a variable voltage to 2 of motor i. This translating op comprise a direct current generator 6 a suitafol means (not shown) having winding 5, a series field winding field winding, such as a shunt field The motor l and the generator 6 a the conventional Ward-Leona tions in the energization of the field I provide an auxiliary dynamit chine it! which is of the armature variably energizing f d ou l generator The armature may he termed an esciter w ch enrol variations in current transmitted to field winding ii. The machine vided with an armature winding videcl with two sets of brushes; on including brushes l3 and are SilC or connected through a conductor ance and provide a path for the s current which produces one com-pom exciting flux of the machine. ct brushes, including brushes l5 and i i voltage which varies as the energl" control field winding l5. Tl across the brushes and i age relative to the voltage 0.: trol field winding ll. Field wi erator is energized from the output of the machine it.

The auxiliary dynamo-electric also he provided with additional in rage. example the machine may have shunt WI Ha which establishes a magnetomo e fore assist that provided by the cross ma force produced by the armature current flowing through the connection between brushes l3 and M. In addition, the machine ill may have a compensating winding llc, the magnetomotive force of which opposes and substantially neutralizes the normal armature reaction. Machine Mi may also be provided with a commutating winding I Id. In order to assure the proper buildup of the voltage of machine l0, auxiliary bias or exciting winding l lb may be connected to produce a magnetomotive force which assists that provided by the compensating winding and the control field winding ll. Certain features of the dynamo-electric machine W are disclosed and claimed in a copending application Serial No. 281,008 of E. F. W. Alexanderson and M. A. Edwards, filed June 4, 1939, and which is assigned to the assignee of the present application.

As an agency for producing a voltage, such as a unidirectional voltage, which varies in accordance with the speed of the motor l, I provide a suitable arrangement, such as a tachometer or'pilot generator ll, comprising an armature winding l8 and a field winding l9. The output of the pilot generator i! may be connected across a voltage divider 20, and a resistance 2| may be connected inseries relation with the voltage divider, In order to provide a source of reference voltage against which the output voltage of the pilot generator ll acts, I employ a suitable arrangement, such as a rectifier circuit 22, which may comprise a transformer 23 energized from a suitable source of alternating current 24 and may include a voltage-doubling type of rectifier cornprising a double-anode electric valve 25, capaci tances 26 and 2? and a suitable constant potential device such as a glow discharge device 28. The voltage appearing across the terminals of the glow discharge device 28 remains substantially constant and serves as a reference potential against which the output voltage of the pilot generator I? acts. A resistance 29 and a capacitance 30 may be connected across the output terminals of the rectifier circuit 22, and an impedance, such as a resistance 31, may be connected between one terminal of the capacitance 30 and the glow discharge valve 28. The potential difierence between conductors 32 and 33 remains substantially constant, and a predetermined component of the constant reference voltage furnished by the glow discharge device 28 is obtained through a voltage divider 34 which is connected to conductors 32 and 33 through a resistance 35. By the adjustment of the voltage dividers 20 and 34, the net voltage or the difierence voltage between the output voltage of the tachometer pilot generator ii and the glow discharge device 28 may be adjusted,

To variably energize the control field winding H of the armature excited machine lo in response to the speed variations of the motor I, and to control the energization of control field winding H to maintain the speed of motor i substantially constant, I provide an electronic regulator The electronic regulator 35 also limits the maximum and minimum current values transmitelectric valve means 31 may be of the high vacuum type comprising an anode 39, a cathode 40,

a control grid 4| and a screen grid 42. The screen grid 52 may be connected to a source of voltage positive with respect to the cathode 40. The voltage applied between the screen grid 42 and the cathode 40 and, of course, the voltage applied between the anode and the cathode may be controlled or adjusted by means of a suitable voltage divider 43 connected across the source 38.

The conductivity of the electric valve means 31 and hence the current transmitted to the control field winding H are determined primarily by the potential impressed on the control grid 4!. This control potential is obtained by means of an impedance element, such as a resistance 44, Variable amounts of unidirectional current are transmitted through theresistance 44 to control the potential impressed on the control grid 4i. To provide a control system in which the conductivity of the electric valve means 31 is controlled selectively in response to two different predetermined controlling influences, I provide a pair of electric circuits energized from thedirect current circuit 33. One of these electric circuits includes a serially connected impedance element, such as a resistance 15, and an electronic discharge device 45; and the othercircuit includes a serially connected impedance element, such as a resistance 41, and

an electronic discharge device 48. Suitable points or connections of the two circuits are employed as points of reference potential. For example, I may employ common junctures 49 and 50 of the resistances 65, ll and electronic discharge devices 46, 18 respectively, as reference points. Electronic discharge devices 46 and 48 are preferably'of the high vacuum type, each comprising an anode 5i, a cathode 52, a control grid 53, a screen grid 54, and a suppressor grid which may be connected to the associated cathode 52.

I employ an electric valve means 56 for selectively controlling the conductivity of the electric valve means 3? from that circuit of said pair of circuits which produces the predominating volt age in response to the respective related controlling influence. That is, the electric valve means 56 is provided with a pair of electric discharge paths associated with anodes 57 and 58 and the electrically common cathodes 59 thereof to energize the resistance it from that circuit of the pair of circuits which produces the predominating control potential. The feature of using a doubleanode or a double-cathode electric valve as a means for effecting selective control from the circuit providing the predominating control voltage is disclosed and claimed in U. S. Patent No. 2,019,352 granted October 29, 1935, upon an application of 0.- W. Livingston, and which is assigned to the assignee of the present application. A capacitance 60 is connected across the resistance 44 to serve as a means for absorbing extraneous voltage variations, Screen grid 54 of electronic discharge device 46 is connected to the lower terminal of resistance 64 through a resistance BI, and is also connected to the anode 39 of electric valve 3? through a resistance 62. These connections afford a feed-back arrangement between the electric valve means 31 and the electronic discharge devices 46 and 48. That is, there is a feedback arrangement between electric valve 3? and discharge device 46 through resistance 62 and the screen grid 54, and there is also a feed-back arrangement between the electric valve 31 and the electronic discharge device 48. These feed-back circuits increase the sensitivity of the electronic regulator 36. Suitable potential adjusting devices, such as voltage dividers 63 and 64, may be associated with the electronic discharge devices 46 and 48, respectively, to adjust the potentials of the respective cathodes and to control the currents conducted through the associated circuits. The voltage divider 63 sets or establishes the maximum current 'limit of the regulator 36, and the voltage divider 64 establishes the minimum current limit for the regulator 36.

The electronic regulator 36 the control field winding H to maintain the speed of the stantially constant value. This operation is effected by controlling the potential of the control grid 53 of the electronic discharge device 46. The variation in the potential of the control grid 53 may be obtained by means of a suitable impedance element, such as a resistance 65, which is variably energized in accordance with the difference between the component of the output voltage of the pilot generator I! and a component of voltage derived from the constant voltage de vice 28. The unidirectional current transmitted through the resistance 65 varies in accordance with the speed of the motor I and controls the potential impressed on the control grid 63. A suitable current limiting resistance 66 may be connected in series relation with the control rid 53.

In order that the electronic regulator 36 maintain the speed of the motor substantially convariably energizes of the machine I6 motor I at a sub stant within a predetermined range of values and in order that the regulator be controlled to limit the maximum and minimum energizations of the armature winding 2 of motor i, I provide a suitable selectivemeans, such as an electric valve means 61, which comprises a pair of electric discharge paths associated with anodes t and 69 and electrically common cathodes 16. Of course, it is to be understood that the discharge current will be carried by the discharge path on which there is impressed the predominating voltage. Anode 68 is connected to one terminal of the pilot generator l1, and anode 69 is connected to be responsive to the energization of the machine I. It will be noted that the anode 69 is connected to the common juncture H of the series field winding 3 and. the armature winding 2 of motor 5. Furthermore, the anode 69 is connected to the control grid 53 of the electronic discharge device 48. The electric valve 61 serves to control the relative amounts of current conducted by electronic. discharge devices 46 and 68, that is, serves to control the relative conductivities of these discharge devices selectively in response to that controlling influence which produces the predominating control potential.

I provide an anti-hunting means connected between the output or armature circuit of the armature excited machine I6 and the electronic regulator 36. This anti-hunting means may comprise a transformer 12 having a secondary winding 13, one terminal of which is connected to conductor 32 and the other terminal of which is connected to the cathode 52 of the electronic discharge device 46 through voltage divider The transformer 12 is connected to modify the regulating action of the electronic'discharge device 46 to prevent over-shooting or under-shooting of the speed of the motor l.

Certain features of the electric valve control. circuit and the armature reaction excited machine are disclosed and claimed in my copending application Serial No. 346,902, filed July 23, 1940. and which is a division of my application Serial No. 280,924.

The operation of the embodiment of my invention shown in the single figure of the accompanying drawing will be explained by considering the system when it is operating to corn trol the speed of the direct current motor l. Of course, it will be understood by those skilled in the art that the speed of the motor I varies directly as the voltage applied to the armature winding 2, assuming that the energization of the field winding 4 remains substantially constant. The variable energization of the control iield winding it controls the excitation of the generator 6 and hence controls the terminal voltage of that generator.

During normal operation, in which the energization of the armature winding i does not exceed the maximum or minimum limit, the control field winding i l is variably energized to maintain the speed of the motor l substantially constant. The electric valve means 3? transmits variable amounts of current from the source 38 to the control field winding H, and the conductivity of the electric valve means 31 is determined by the potential appearing across the terminals of resistance 44. So long as the aforesaid current limits are not exceeded, the variations in speed of the motor l produce corresponding variations in the output voltage of the pilot generator it to cause variations in the amount of unidirectional current transmitted through resistance Of course, during normal operation the discharge current is conducted between anode and oath-- ode i6 and the variable control potential is impressed across control grid 53 and cathode As the speed varies, the conductivity of the electronic discharge device it also varies the potential of connection it is raised or lowered to control the amount of current transmitted through resistance 44 which, in turn, controls the conductivity of the electric valve For example, if the speed of the motor 5 tends to increase above a desired value, the generated voltage produced by the pilot generator i'i also increases, thereby causing an increase of current transmitted through resistance t5. An increase in current transmitted through the resistance raises the potential impressed on control grid of electronic discharge device @6 and, since the current through the resistance at is increased, the potential of the juncture 39 will be lowered. Consequently, the current transmitted through resistance 44 will be decreased and the conductivity of the electric valve means 3? will be correspondingly decreased. In this mariner, the amount or" current transmitted to the control field winding ii is decreased, effecting a reduction in the current transmitted to field winding e of generator 6. As a result, the voltage applied to the armature winding 2 of motor 3 is decreased and the speed will be restored to the desired value. Conversely, as the speed of the motor i tends to decrease, it will be understood that the energization of the control field winding i! will be increased by the electronic regulator 36 to raise the speed of the motor I to the desired value.

During the above described normal range of operation, the current transmitted to the resistance fll is, of course, conducted through a path including anode 58 of the electric valve means 5d. The electronic discharge device 48 is maintained conductive during the normal range of operation to such an extent that the potential of the common juncture 50. and that of the anode 51 of electric valve means 56 are lower or negative relative to the potential anode 58.

The electronic regulator-38 also operates to limit the maximum energization of the armature winding of motor I in the following manner: it the current transmitted to the armature winding 2 of motor I tends to exceed a predetermined value, the potential of the common juncture H of the armature 2 and field winding 3 rises, causing the control to be transferred from anode 88 to anode 69 of the electric valve means 6?, in which case the control of the pilot generator H is rendered ineffective. The potential of the control grid 53 of electronic discharge device 46 is limited so that the maximum current transmitted. to the control field winding lI remains substantially constant, thereby limiting the energization of the armature winding 2 of motor l. The operation of the regulator 36 which limits the maximum energization of the armature winding of motor 2 may be explained in the fol-= lowing manner. When the energization reaches a predetermined maximum value, causing anode oil of the electric valve 61 to conduct, a circulating control current flows through a circuit including anode 59, cathode l0, resistance to, armature l of generator 6 and armature 2 of motor I. It will be noted that the left-hand terminal'of voltage divider 63 is connected. to the negative terminal of circuit 38. Ii the current tends to increase above the maximum value, the circulating current temporarily increases and conductivity of the electronic discharge device 46 will be temporarily increased, eiiecting a reduction in the potential of anode 58 of electric valve to and efiecting a corresponding decrease in the conductivity of the electric valve means til. Consequently, the current transmitted to motor will be decreased to the desired value. The potential applied to grid $3 of discharge device do under these conditions is the diflerence between the voltage drop across field windings 3 and 8 and the potential difierence between the cathode E22 and the negative terminal of circuit iii). Therefore, the maximum potential variation of the grid 58 with respect to the cathode is limited to set a maximum limit to the current supplied to armature winding 2. The setting of the voltage divider 68 establishes the value of the maximum limit.

The electronic regulator 38 also operates tolimit the minimum energization of the armature winding 2;, thereby preventing a regenerative action between the motor I and the generator 6. it the armature current transmitted to motor I decreases below a predetermined value, it will be noted that the potential of the control grid c3 of the electronic discharge device 38 is lowered, effecting a substantial decrease in conductivity of the electronic discharge device 48. As a result, the potential of the juncture 56 will rise, causing the potential of anode 5'! of the electric valve 5% to become more positive than that of the anode and eiiecting a transfer in control to electronic discharge device 48 from the electronic discharge device it. In this manner, a minimum conductivity in the electric valve means 31 is assured and consequently a predetermined minimumcurrent is assured tor the energization of the control field. winding II. The energization of the armature winding of the motor I, therefore, is maintained at or above a predetermined minimum value. The value of the minimum current transmitted to the armature winding 2 is established by the setting of the voltage divider 64 since it determines the potential of the cathode 52 of discharge device 48.

The anti-hunting means, including the transformer 12, serves to prevent over-shooting of the regulatory action of the electronic regulator 36. The operation and the efiect of the anti-hunting means may be explained in the following manner. If it be assumed that the electronic regulator dictates an increase in the energization of the control field winding iI,-the transformer I2 is connected to impress a transient positive voltage on the cathode 52 of the electronic discharge device 15, thereby tending to decrease the corrductivity of this discharge device and eflecting a stabilizing action which tends to prevent overenergization of the control field winding II. Of course, if the electronic regulator 36 dictates a decrease in energization of the control field winding it, the transformer 12 impresses a transient negative voltage on the cathode 52 of electronic discharge device 46, thereby tending to prevent an under-shooting of the energization of the control field winding BI. That is, the anti-hunting means acts as a stabilizing means to efiect a more precise control of the speed of the motor I under transient load conditions.

The feed-back connection between the anodecathode circuit of the electric valve means 31- and the screen grid 54 01 the electronic discharge device 38 enables the regulator 36 to maintain accurately the speed of the motor 2, inasmuch as the circuit increases the sensitivity of the regulatory action. This effect, which is a positive feed-back, may be appreciated by considering the regulator 36 under these conditions when the electronic discharge device #6 is controlled by an increase of potential on the control grids 5t, tending to increase the conductivity of the discharge device. Upon such increase in the current conducted by the discharge device 46, the voltage impressed on the control member 4| of electric valve Bl will be decreased effecting a temporary rise in potential of the anode 39. This rise in potential of the anode raises the potential of screen grid 55 and accordingly increases the sensitivity of the regulator.

The armature excited machine it) operates as an electromagnetic amplifier; that is, small variations in the current transmitted. to the control field winding I l produce a highly amplified variation in the output of machine Ill. Th control field winding It produces a magnetomotive force having a component displaced 9% electrical degrees relative to the cross magnetomotive force produced by the short-circuit current which flows in the armature winding 52 due to the connection between brushes I3 and It. The object of the control field winding H is to permit the output voltage appearing across brushes I5 and it to be varied without introducing additional controlling means in the armature circuit. The control field II effects control of .the current output of the armature winding I2; and, as stated above, there is obtained a substantial amplifying effect hetween the energization of the control field winding H and the output circuit of the machine it. The value of th output current of machine iii, for a given input voltage impressed across the control field winding i i, may be varied by varying the control field current. Of course, it is to be understood that the armature excited machine I0 is driven mechanically. In the embodiment of the invention shown, the armature of the machine lfl may be connected mechanically to the enerator 6 or to the means which drives the generator 6. The machine Ill responds very rapidly to changes in field energization to produce changes in output current. Of course, the input current or changes in input current will be amplified.

While I have shown and described my invention as applied to a particular system of connections and as embodying various devices diagrammatically shown, it Will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention and I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a source of current, a load circuit, electric valve means connected between said source and said load circuit for controlling the current transmitted to said second circuit, said electric valve means having a control memher, an impedance element, an electronic discharge device of the controlled type for transmitting variable amounts of current from said source through said impedance element to control the voltage impressed on said control member, means for controlling the conductivity of said electronic discharge'device, a second electronic discharge device for transmitting variable amounts of unidirectional current from said source through said impedance element, a pair of unidirectional conducting paths connected between said first mentioned and said second mentioned electronic discharge devices and said impedance element for selectively deriving contr-ol from that discharge device providing the predominating control voltage, and means for controlling the electronic discharg devices comprising a second pair of unidirectional conducting paths selectively responsive to two difierent pre determined controlling influences.

2. Incombinaticn, a source of current, a load circuit, electric valve means connected between said source and said load circuit for controlling the current transmitted to said second circuit, said electric valve means having a control member, means for producing a plurality of relatively variable control potentials which are responsive respectively to different predetermined controlling influences, an impedance element, an electric valve means having a pair of electricdischarge paths connected in circuit with said impedance element, an electronic discharge device of the controlled type for controlling the voltage impressed across one of the discharge paths of said electric valve means to transmit variable amounts of current through said impedance element and to impress a variable control potential on said control member, a second electronic discharge device of the controlled type for impressing across the other of said discharge paths a control potential, and means for controlling the electronic discharge devices comprising electric valve means having a pair of discharge paths selectively responsive selective control of said electric valve nating control potential con-'1 to that controlling influence providing the dominating control potential.

3. In combination, a source of direct current, a load circuit, an electric valve means having a comm trol member for transmitting variable amounts of current to said load circuit from said Source, a pair of electric circuit for producing control potentials and connected to be energized om said source and each comprising a serially eonnected resistance and an electronic discharge device of the controlled type comprising at least one control grid, means for energizing the control grids, and means connected between said circuits and said control member for effecting means from that circuit producing the predominating control potential comprising an impedance element and an electric valve means having a pair of electric discharge paths each of which is associated with a difierent one of said electric circuit.

4. In combination, a source of direct current, load circuit, an electric valve trol member for transmitting variable amounis of current to said load circuit from said source, a pair of electric circuits for producing control potentials and connected to be energized from said source and each comprising a serially connected resistance and an electronic discharge device of the controlled type comprising at least one control grid, means connected between said circuits and said control member for effecting selective control of said electric valve means from that circuit producing the predominating control potential comprising an impedance element and an electric valve m ans having a pair of electric discharge paths each of which is associated with. a different one of said electric circuits, means for producing two relatively variable control potentials which are responsive respectively to two different controlling influences, and means for ef fecting selective control of the relative conduc tivities of said first mentioned and said second mentioned electronic discharge devices through the associated control grid in response to the predominating control potential or" said last mentioned control potentials and comprising an elec tric valve means having a pair of electric dispaths each of which is responsive to a different one of said last; mentioned control potentials.

5. In combination, a source of c rrent, a circuit, an electricvalve means having an a cathode and a control member for transmit variable amounts of current to said load oircun from said source, a pair or" electric circuits ior producing control potentials and connected to be energized from said source and each comprising a serially connected resistance electronic discharge device oi the controlled t comprising a pair of control grids, means energizing one control grid of each of the charge devices, means connected between pair of circuits and said control member for e fecting selective control 0" said electric r c means from that circuitpri cing the pro sing an imperial c; element and an electric valve means havin pair of electric discharge In? hs each or" which s associated with a diiieent one of said elec circuits, and a feedback c rcuit connectec tween the anode-cathode circuit of said first m tioned electric valve means and the other control grid of at least one of the electronic discharge devices.

5. In combination, a source of current, a loa means having a com for impressing on one or said control grid :1 voltage variable in response to a predetermined controlling influence, and a feed-back means connected between the anode-cathode circuit of said electric valve means and the other control grid.

JERRY L. STRA'ITON. 

